Control circuit



NOV. 19, 1946. J; c s 2,411,358

CONTROL CIRCUIT Filed Sept. 19, 1944 FELL 27 H may ,7 7' Load k:lllllllli- WITNESSES: lNVENTOR 5 4 jg HarryfB'c/vsel.

ATTORNEY Patented Nov. 19, 1946 UNITED STATES PATENT OFFICE CONTROLCIRCUIT Harry J Bichsel, Pittsburgh, Pa., assignor to WestinghouseElectric Corporation, East PittsburglnPaL, a corporation of PennsylvaniaApplication September 19, 1944, Serial No. 554,783

6 Claims. (Cl. 315-274) This invention relates to an electric dischargevalve of the arc-like type and has particular relation to controlapparatus for rendering the valve conductive.

Electric discharge valves of the arc-like type, such as thyratrons,include an anode, cathode and a control electrode. It is a well knowncharacteristic of such valves that they remain nonconductive as long asthe control electrode-tocathode voltage is less positive than a predetermined critical voltage. If an anode-to-cathode voltage exists which isgreater than the breakdown voltage of the valve, with the anodepositive, the valve becomes conductive the instant the controlelectrode-to-cathode voltage becomes more positive than the criticalvoltage. The control electrode then loses control of the valve whichcontinues to conduct until the anode-tocathode voltage is reduced belowthe arc drop of. the valve. This feature is employed widely where it isdesired to render the valve conductive at a predetermined instant. Oftenan alterhating potential or other potential having a steep-wave front isimpressed between the control electrode and cathode so that the instantat which the control electrode becomes more positive with respect to thecathode than the critical voltage may-be accurately predetermined. Apeaking transformer energized from an alternating potential source isfrequently used for this purpose. Such arrangements ordinarily operatequite satisfactorily. However, under certain conditions seriousdifiiculties are encountered. In a number of cases it is desirable torender a valve conductive at the instant that-some other operation takesplace, for, example, when a relay is operated Under such circumstances,it has been customary to provide a voltage which is applicable to thecontrol electrode. and cathode upon the closure of the relay contacts.Frequently a precharged capacitor is discharged through a dischargecircuit including the primary of a peaking transformer when relaycontacts in the discharge circuit-are closed, the secondary winding ofthe peaking-transformer being connected in circuit betweenthe controlelectrode and cathode of the valve. Howev,er, it has been found thatsuch an arrangement is unreliable in that it occasionally fails torender the valve conductive at the instant desired. e r it ,.,It,isaccordingly an object of my invention to providea: novel controlarrangement for an electri dischargefvalve. of the arc-like type forrender gfbll; valve conductive at a desired instant. nnother object ofmy inventionisto provide a novel control arrangement for rendering anelectric discharge valve of the arc-like type conductive at a desiredinstant, which arrangement is highly reliable in operation.

A further object of my invention is .to provide a new and improvedcontrol arrangement for rendering an electric discharge valve of thearclike type conductive at an instant determined by the operation of arelay.

My invention arises from the realization that the occasional failures inprevious systems as described was caused by the bouncing of the contactsof the relay. The contacts of most relays other than very specialexpensive relays, bounce upon closing. This bouncing causes adiscontinuity in the voltage impulse which is applied be-- tween thecontrol electrode and cathode of the valve in the prior arrangements.contacts bounce at the right moment, the peak portion of the voltageimpulse may be missed completely, so that the valve is not renderedconductive.

In accordance with my invention, a biasing potential is impressedbetween the control electrode and cathode of the valve tending tomaintain the former less positive with respect to the latter than thecritical voltage of the valve. An energy storage device is connected inparallel circuit relation with an impedance, such as a resister, and theparallel storage device and impedance are connected in a series circuitwith a normally closed switch which may be the contacts of a relay. Adirect current is then supplied through the series circuit and serves tostore up energy in saidstorage device. When the switch is thereafteropened, the energy so stored is released to eifect current flow throughthe impede ance. Means are provided to make the control electrode morepositive with respect to the cathode than the critical voltage andthereby render the valve conductive in response to the release of theenergy. Since the valve becomes conductive upon the opening of theswitch, the bouncing of the contacts if the switch is formed by thecontacts of a relay obviously does not affect the instant of firing ofthe valve.

The novel features whichI consider charac- If the relay V tron, has itsanode and cathode i connected in a circuit extending from the anodethrough a.

normally closed pushbutton switch, 9, a load NY and a source ofpotential such: as a battery [3;

to the cathode. The battery [3 produces a'volt age between the anode 5and the cathode i which is greater than the breakdown voltage of thevalve, with the anode 5 being positive.

The control electrode or grid E5 of the valve 3 is connected to thecathode 'i. in a circuit which,

extends from the grid through a grid'resistor; H, the secondary windingit of a transformer 21, and a source of biasing potential such-as abattery 23 to the cathode. In addition a loading resistor 25 isconnected in shunt across the secondary winding iii. The battery 23tends to maintain the grid less positive with respect to the oathode, 7'than the critical voltage of the valve, and thus maintain the valvenon-conductive.

The primary winding 21' ofthe transformer 2! is connected across asource of direct-current potential 29 through an adjustable resistor 31and the normally closed contacts 33 of a relay 35. Another resistor 34is connected in shunt across the primary winding 21.

The sourceof'direct-ourrent potential 29 is illustrated as a resistorwhich is supplied from alternating potential supply lines 36 and 31through a transformer 3%, a full wave rectifier il and-"a filteringcapacitor 43,. Any other source of direct-current potential of theproper magnitude and polarity may, of course, be used.

' The contacts 33 of the relay 35 may be opened by energization of therelay coil 45. This coil is illustrated as connected in circuit with anormally open push-button switch 41 across the alternating potentialsupply lines 36 and 31.

- While the relay contacts 33 are closed, direct current flows from thesource 29 through the contacts 33, adjustable resistor 3!, and theparallelconnected primary winding 2'! and resistor 34. Since theimpedance of the resistor 34 is high compared to the impedance of theprimary winding 21, most of the current flows through the primarywinding and stores up energy in the transformer. If push-button switcht! is then closed, relay coil 45 is energized and contacts 33 areopened. As a result, the supply of direct current is interrupted and theenergy storedin the transformeris released. Some of the energy soreleased tends to keep thecurrent flowing through the primary winding 2!in the same direction as the current previously supplied from the source29 because of the inductive eifect of the primarywinding." Consequently,current flows in the circuit made up-of the primary winding 21 and theresistor 34.

The rapid chan'ge'of flux in the transformer caused by the release ofenergy stored therein produces a voltage impulse across the secondarywinding 59 which is of such polarity and magnitude as to overcom'ethebiasing potential ofthe 4 zero and the valve 3 becomes nonconductive. Ifthe push-button switch 9 is then allowed to reclose, the valve may berendered conductive again by reclosure of the push-button switch 41.

The purpose of the adjustable resistor 3| in circuit with the primarywinding 21 is to limit the magnitude of the direct current suppliedthrough the primary winding to the; value permissible with theparticular transformer employed. It is therefore understandable that theright end of resistor 34 may be connected to any point, along thecircuit between the contacts 33 and the right-hand end of primarywinding 21 without changing the operation of the circuit if the .valueof, the resistor is selected properly in accordance with the point ofconnection.

It is also to be understood that while switches 9 and 4.1 are shown aspush-button switches, various other well known means may be employed toefiect energization and deenergization ofthe corresponding circuits.Contacts33'may also be replaced with other switch means if desired, thevalve being rendered conductive uponthe opening of such other switchmeans. It isalso to be noted that an alternating potential may beemployed in the anode circuit of the'valve in place of the battery l3;Under such circumstances energization of the relay 35 should becoordinated with the alternating potential to occur during the halfperiod in which the anode 5 of the valve is positive.

While I have shown and described a specific embodiment of my; invention,I am well aware that many modifications thereof are possible withoutdeparting from the spirit of the invention. It is not my intentionthereforeto limit my invention to the specific embodiments'hown.

I claim as my invention?" ,1. Control apparatus for an electricdischarge valve of the arc-like type having an anode, cathode andcontrol electrode, comprising a control, circuit connected from saidcontrol electrode to said cathode and including biasing potential meanstending to maintain the former less positive with respect to the latterthan the critical voltage of the valve, an energy storage device,impedance means connected in parallel circuit relation with said device,a normally closed switch connected in a series circuit with saidparalleled device and impedance means, and means adapted to supplydirect current through said series circuit, whereby energy stored insaid device by said direct current is released to effect current fi'ow'through said impedance means when said switch is opened, said control,circuit: being coupled to said device to make said control electrodemore positive withrespect to said cathode than said critical'voltage inresponse to the release of said energyf 2. Controlapparatus for anelectric discharge valve of the arc-like typ having an anode, cathodeandcontrol electrode, comprising atransforme having a primary and'a'secondary wind ing, circuit means connecting "said secondary winding in'a' circuit between; said control" electrode and cathode includingbiasing potential- .means'tending to maintain the control electrode lesspositive with respect to the cathode than the critical voltage ofsa'idvalve, impedance means connected in parallel circuit relation withsaid primary winding, a normally closed switch connected in a seriescircuit'with said paralleled im-; pe-dance means and primary winding,and means adapted to supply direct current through said series circuitof such polarity that the'rele ase '5 of energy stored thereby in saidtransformer, as effected by opening of said switch, causes a voltageimpulse across said secondary winding to render said control electrodemorepositive with respect to the cathode than said critical voltage. 3.Control apparatus for an electric discharge valve of the arc-like typehaving an anode, cathode and control electrode, comprising a transformerhaving a primary and a secondary winding, circuit means connecting saidsecondary Winding in a circuit between said control electrode andcathode including biasing potential means tending to maintain thecontrol electrode less positive with respect to the cathode than thecritical voltage of said valve, impedance means connected in parallelcircuit relation with said primary winding, a relay having normallyclosed contacts connected in a series circuit with said paralleledimpedance means and primary winding, means adapted to supply directcurrent through said series circuit, and means for operating said relayto open said contacts, the polarity of said direct current being suchthat the release of energy stored thereby in said transformer, asefiected by opening of said contacts, causes a voltage impulse acrosssaid secondary winding to render said control electrode more positivewith respect to the cathode than said critical voltage.

4. Control apparatus for an electric discharge valv of the arc-like typehaving an anode, cathode and control electrode, comprising a transformerhaving a primary and a secondary winding, circuit means connecting saidsecondary winding in a circuit between said control electrode andcathode including biasing potential means tending to maintain thecontrol electrode less positive with respect to the cathode than thecritical voltage of said valve, a resistor connected in parallel circuitrelation with said primary winding, a normally closed switch connectedin a series circuit with said paralleled resistor and primary winding,and means adapted to supply direct current through said series circuitof suchpolarity that the release of energy stored thereby in saidtransformer, as effected by opening of said switch, causes a voltageimpulse across said secondary winding to render said control electrodemore positive with respect to the cathode than said critical voltage.

5. A control system comprising an electric discharge valve of thearc-like type having an anode, cathode and control electrode, means forimpressing a positive voltage between said anode and cathode, a controlcircuit connected from said control electrode to said cathode andincluding biasing potential means tending to maintain the formerlesspositive with respect to the latter than the critical voltage of thevalve, an energy storage device, impedance means connected in parallelcircuit relation with said device, a normally closed switch connected ina series circuit with said paralleled device and impedance means, andmeans adapted to supply direct current through said series circuit,whereby energy stored in said device by said direct current may bereleased to efiect current flow through said impedance means when saidswitch a is opened, said control circuit being coupled to said device tomake said control electrode more positive with respect to said cathodethan said critical voltage in response to the release of said energywhereby said valve is rendered conductive when said switch is opened.

6. A control system comprising an electric discharge valve of thearc-like type having an anode, cathode and control electrode, means forimpressing a positive voltage across said anode and cathode, atransformer having a primary and a secondary winding, circuit meansconnecting said secondary winding in a circuit between said controlelectrode and cathode including biasing potential means tending tomaintain the control electrode less positive with respect to the cathodethan the critical voltage of said valve,

a resistor connected in parallel circuit relation with said primarywinding, a normally closed switch connected in a series circuit withsaid paralleled impedance means and primary Winding, and means adaptedto supply direct current through said series circuit of such polaritythat the release of energy stored thereby in said transformer, aseffected by opening of said switch, causes a voltage impulse across saidsec ondary winding to render said control electrode more positive withrespect to the cathode than said critical voltage whereby said valve isrendered conductive when said switch is opened.

HARRY J. BICHiSEL.

